1. Field of the Invention
The present invention concerns a method for sound-object oriented analysis and note-object oriented processing of polyphonic sound recordings.
2. Description of Related Art
It has long been known to subject acoustic recordings having a musical content to sound-quality post-processing. In earlier days such studio techniques were carried out resorting to expensive hardware equipment such as complex filter banks; nowadays on the other hand computers and special computer programs are used, which are far more economical and are accordingly more widespread. Further advances incorporate digital recording. In general the purpose of such post-processing is to improve the recordings' sound quality or to incorporate sound effects into them. Such sound post-processing operates in purely effect-oriented manner and might not detect the signal's musical content, instead construing the audio signals being merely a time-varying signal amplitude.
A method and equipment to change the sound and the pitch of audio signals are known in the state of the art, for instance from the European patent document EP 0 750 776 B1, respectively the German patent DE 696 14 938 T2. Such disclosures are considered as incurring the drawback that they preclude operating with complex sound materials such as occur in conventional musical productions.
Processing audio material is desirable at the level of the individual notes making up the sound recording. It is known from the state of the art to extract single notes with note pitches, note lengths and time of occurrence from an audio recording's. Such a note extraction illustratively is known from the German patent document DE 10 2004 049 477 A1 to determine a melody line of an audio signal. The transformation of an audio signal into a note-based description is known from the patent document WO 02/084641 A1, for the purpose of allowing reference of the audio signal in a databank. Processing the extracted notes, for instance by frequency changes or time shifts, does not take place. Said documents cite a further state of the art.
It is especially critical, when processing audio material, that the original sound perception, for instance of a singing voice, shall be preserved also following said processing. This feature is attained in an outstanding manner in the state of the art's “Melodyne” software made by Celemony Software GmbH, and it uses a note-based procedure. However this software presumes the material contains unison material. Chordal instruments such as guitars, pianos, or choral songs, heretofore could not be processed by means of tones. So far such chordal recordings could only be processed in chordal segments or by time stretching processed in time or in the note pitch, however without access to individual tones of a chord. It was impossible to change a single chord note (for instance the E of a C major chord illustratively into E minor for C flat) unless the other chord tones were simultaneously processed as well.
Chord recognition and approaches identifying individual notes are already known from the state of the art, though used to print notes (WIDI software) or to automatically recognize titles (German patent document DE 10 2004 049 477 A1).